Evidence for two distinct anisotropies in the oxypnictide superconductors SmFeAsO_(0.8)F_(0.2) and NdFeAsO_(0.8)F_(0.2)

Abstract

Single crystals of the oxypnictide superconductors SmFeAsO_(0.8)F_(0.2) and NdFeAsO_(0.8)F_(0.2) with T_c in the range of 44 K to 48 K were investigated by torque magnetometry. An analysis of the data in terms of a recently proposed model for the anisotropic magnetization in the superconducting state, treating the penetration depth anisotropy differently than the upper critical field anisotropy, provides evidence that in the oxypnictide superconductors two distinct anisotropies are present. As a result the penetration depth anisotropy differs significantly in magnitude and in temperature dependence from the upper critical field anisotropy, analogous to MgB_2 but with a reversed sign of slope. This scenario strongly suggests a new multi-band mechanism in the novel class of oxypnictide high-temperature superconductors.

published online in J. Supercond. Nov. Magn

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• Superconductivity at 23 K and Low Anisotropy in Rb-Substituted BaFe_2As_2 Single Crystals
• Th substituted SmFeAsO: structural details and superconductivity with Tc above 50 K
• Experimental evidence for a two-band superconducting state of NbSe2 single crystals
• Anisotropic Phase Diagram and Superconducting Fluctuations in SmFeAsO0.85F0.15
• Corrected Entropy of Friedmann-Robertson-Walker Universe in Tunneling Method
• Intrinsic and extrinsic pinning in NdFeAs(O,F): vortex trapping and lock-in by the layered structure
• Quantum Oscillation Studies of the Fermi Surface of LaFePO
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• Anisotropy of the superconducting state parameters and intrinsic pinning in low-level Pr-doped YBa2Cu3O(7-delta) single crystals
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